1. Field of the Invention
The present invention relates to a semiconductor package including a through-hole electrode and light-transmitting substrate, e.g., a camera module.
2. Description of the Related Art
As electronic apparatuses become smaller, semiconductor devices to be incorporated into these electronic apparatuses must also be made smaller and more highly integrated. In the second half of the 1990's, the examination of putting a wafer level chip scale package (to be referred to as a wafer level CSP hereinafter) into practical use began (e.g., “Nikkei Micro Devices”, April 1998, pp. 28, 164, and 176). In this package, a semiconductor chip is connected to a substrate by bumps with the chip surface facing down by using a flip-chip method using no lead wire.
On the other hand, a stacked package (multi-chip package) capable of achieving a very small size by three-dimensionally stacking a plurality of semiconductor chips has been developed since the last half of the 1990's, and a package using a through-hole electrode has been proposed (e.g., Jpn. Pat. Appln. KOKAI Publication No. 10-223833). The examination of the wafer level CSP of an optical element has begun around 2000. The structure of glass+adhesive layer+image sensor+through-hole electrode formed by Koyanagi et al. and a sectional photograph of the actually formed structure are described in “International Electron Devices Meeting 1999 Technical Digest”, pp. 879-882. U.S. Pat. No. 6,489,675 has also disclosed the sectional structure of an optical element including a through-hole electrode and light-transmitting substrate. In any through-hole electrode, an electrode pad layer exists on the bottom of the through-hole electrode, and the electrode pad functions as a stopper for a via formed in silicon by anisotropic etching.
When forming the wafer level CSP of an optical element, the optical element is first formed in the form of a wafer, and whether each chip is good or bad is checked by a die sort test. In this test, the needle of a die sort tester touches an electrode pad in the uppermost layer of the optical element, and leaves a mark on the electrode pad. When the section of the mark on the electrode pad is observed, the electrode pad is largely scooped out into the form of a recess. If there is only one electrode pad layer and this electrode pad is used not only for the die sort test but also as the anisotropic etching stopper, a portion damaged and thinned by the die sort test does not function as the stopper any longer, and anisotropic etching breaks through the electrode pad.
To avoid this inconvenience, it is necessary to separately form an electrode pad for use in the die sort test and an electrode pad to be used as the anisotropic etching stopper. Jpn. Pat. Appln. KOKAI Publication No. 2007-53149 describes a structure in which two or more electrode pad layers are formed in an interlayer insulating film, and a contact plug electrically connects an element surface electrode in the uppermost layer and an internal electrode serving as an anisotropic etching stopper when forming a through-hole electrode, although the structure is not an optical element.
Unfortunately, this structure is a very rigid structure in which the contact plug exists over the entire surfaces of the internal electrode and element surface electrode. When the needle of the die sort test touches the element surface electrode of this structure, the electrode may sink into silicon and destroy the element because the electrode is too rigid. Also, if the needle and electrode are strongly adhered, the whole electrode may be removed together with the needle from the silicon substrate when the needle is removed.